Remove support for libmysql-client from mysqli test suite

Since mysqli can no longer be built against libmysql-client, there is
no longer the need to distinguish.

While we're at

Remove support for libmysql-client from mysqli test suite

Since mysqli can no longer be built against libmysql-client, there is
no longer the need to distinguish.

While we're at it, we also drop the superfluous is_object() checks.

Closes GH-9652.

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Fix libmysql test cases (#7097)

Fixed test cases for: mysqli_stmt_execute_bind_libmysql, bug77935, fetch_column, and some others that failed on libmysql

Port skipif.inc files to EXTENSIONS

Implement mysqli_fetch_column (#6798)

* Implement mysqli_fetch_column